1. Field of the Invention
The present invention relates to an optical property altering apparatus.
2. Description of the Related Art
In general, imaging apparatuses, such as compact digital cameras and monitoring cameras are among devices employing small lenses include. In such imaging apparatuses, a given lens in the optical system is moved along the optical axis, or if digital processing is possible, captured image data is digitally processed and image expansion/reduction processing is executed. Image focusing is typically performed by the movement of a focusing lens. Further, aberration occurs in a lens as a consequence of refractive index differences related to optical wavelength. Thus in an effort to eliminate aberration, the curved surface of a given lens in the optical system is formed to into an aspheric surface derived from a polynomial expression.
However, for zoom and focus functions provided in conventional imaging apparatuses, a lens is mechanically moved and thus, as a result of mechanical instability, optical axis deviation, optical axis, tilt, lens tilt, etc. occur and consequently, is linked to deterioration of the image quality. Furthermore, there is a problem of differences among elements as a cumulative result of manufacture tolerances. On the other hand, problems arise even if an aspheric lens is employed. For example, if the aspheric lens is fabricated by a glass mold, high precision fabrication technology is required. Further, if an aspheric surface is created by a compound lens, an aspheric shape must be formed on a glass lens using, for example, a UV curable resin, inviting additional fabrication steps.
On the other hand, telescopes provided at observatories and the like are devices that employ large lenses. The Subaru Telescope at an observatory in Hawaii is a classic example. This telescope is a large reflecting telescope, whose most important element, the primary mirror, is said to have a 14 nm planar grind tolerance, extremely high planar precision. Furthermore, the primary mirror is fabricated to be thin for weight reduction and from a back side, is supported by 261 actuators to sequentially correct distortion of the primary mirror resulting from orientation. With respect to atmospheric distortion, a prism having a structure substantially identical to that of the primary mirror is inserted into the optical path and the prism is deformed in such a way to negate the distortion and facilitate the sequential correction.
However, with such telescopes achieving high resolution by a single primary mirror, the primary mirror must have extremely high planar precision and thus, an apparatus that corrects distortion of such a primary mirror must be uniquely fabricated according to the properties of the primary mirror, making versatility extremely low. If atmospheric distortion is corrected by a technique similar to that for correcting distortion of the primary mirror, additional optical elements such as a prism for correction become necessary and, luminance and saturation of that amount alone decrease. Further, if the number of optical elements increases, the rate of failure increases.
To solve such problems, the development of “plasmonic metamaterials” (metamaterials) is in progress. A metamaterial is an element that achieves optical property improvement and has an optical property that does not conventionally exist. For example, Tanaka, Takuo, et al in “Design of Plasmonic Metamaterials in the Visible Light Region”, Optical Society of Japan, Kogaku Journal, Vol. 6, No. 10, 2007, pp. 584-589, discloses an attempt to create an element having a negative refractive index by creating a fine structure on a surface of an optical element and by using the dielectric constant of the material used for the structure and unique permeability obtained from the arrangement of the structure. Further, Japanese Patent Application Laid-Open Publication Nos. 2007-226033, 2007-256929, 2006-301345, and 2005-260965, for example, propose technology that improves optical properties using a metamaterial.
To solve the above problem associated with the small lens, demand exists for a means to change the focal length of an optical system without the movement of an optical element. Further, demand exists for provision of a function that by an optical element obtains an effect equivalent to an aspheric lens.
However, the technologies disclosed in the above patent documents fail to solve the problems associated with the above conventional technologies. That is, the technologies disclosed in Japanese Patent Application Laid-Open Publication Nos. 2007-226033, 2007-256929, and 2006-301345 respectively involve setting, in advance, the refractive index to become a given value (negative refractive index) to design and fabricate an element, making the refractive index unchangeable after fabrication. Hence, variation of the focal length of an optical system is impossible without moving an optical element. Further, since a uniform refractive index distribution is imparted for an optical element, for example, it cannot be said that an effect equivalent to an aspheric lens will be achieved by making the refractive index distribution non-uniform.
Further, the technology disclosed in Japanese Patent Application Laid-Open Publication No. 2005-260965 is able to vary the refractive index. However, this technology is limited to use in a radio wave area and merely switches between a common property and a property as that of a metameterial and hence, the above problems associated with a small lens are not solved.
On the other hand, to solve the above problems associated with a large lens, it is preferable for optical system distortion and atmospheric distortion to be addressed using an optical element facilitating versatility.
However, the technologies disclosed in the above patent documents fail to solve the problems associated with the conventional technologies. That is, the technologies disclosed in Japanese Patent Application Laid-Open Publication Nos. 2007-226033, 2007-256929, and 2006-301345 respectively involve setting, in advance, the refractive index to become a given value (negative refractive index) to design and fabricate an element, making the refractive index unchangeable after fabrication. Hence, the refractive index cannot be changed in real-time and thus, in particular, distortion resulting from a difference in orientation cannot be corrected as circumstances dictate. Further, since the refractive index cannot be changed in real-time, atmospheric distortion cannot be corrected.
The technology disclosed in Japanese Patent Application Laid-Open Publication No. 2005-260965 can vary the refractive index. However, this technology is limited to use in a radio wave area and merely switches between a common property and a property as that of a metameterial and hence, cannot correct optical element distortion and atmospheric distortion.